Ammonia is a material that must direct attention to the importance of its management. Notably, ammonia attracts attention in the environment and energy fields. In the energy field, the synthesis of ammonia with the aid of renewable energy or the like is now considered. Optionally after stored in the form of chemical energy, the ammonia may be turned immediately into fuel or hydrogen may be removed out of the ammonia for fuel production (Patent Publication 1). In the field of biomass power generation, on the other hand, livestock's feces and urine or the like are fermented to turn methane into fuel, but most of the ensuing nitrogen content remains as ammonia in the digestive fluid, and how to make use of or process that ammonia is now under study (Patent Publication 2).
Meanwhile, a main ingredient of PM 2.5 that is a fine particle of less than 2.5 μm is known to be ammonia ions in the environmental field (Non-Patent Publication 1). A possible origin for this ammonia may be dissipations from farmlands, etc., and it is pointed out that stricter management may be applied to such dissipations from now on (Non-Patent Publication 2). Further, increased concentrations of ammonia in water may have an adverse influence on aquatic life; according to the established water criteria for fisheries, for instance, ammonia must have a very low concentration of as low as 0.01 mg/L for fresh water and 0.03 mg/L for seawater (Non-Patent Publication 3).
In other fields than the environmental and energy fields, a problem with ammonia is that it may remain as impurities in semiconductor productions and within fuel cells; there is a need for its removal. In addition, ammonia is often used for removal of nitrogen oxides out of exhaust gases; there is a challenge about how to address a problem arising from excessive addition of ammonia (for example, see Patent Publication 3).
Ways of how to manage such ammonia include exploitation of an ammonia adsorbent.
Ammonia adsorbents that have gained renown so far in the art are compounds including metals capable of forming ammine complexes such as calcium chloride (ammine complex-forming compounds, zeolite or similar materials.
In a possible process for occluding ammonia using an absorbent, ammonia is adsorbed onto the adsorbent, and pressures or temperatures are then controlled for dissipation of ammonia. However, the aforesaid ammine complex-forming compound changes largely in volume between the times of occlusion and desorption of ammonia, resulting in a problem that, for instance, even pulverization of that compound causes disintegration of particles as occlusion and desorption are repeated (Non-Patent Publication 4).
A problem with zeolite is on the other hand that volumes of adsorption are as low as 5 to 9 mmol (ammonium nitrogen per g of absorbent), although there have been studies of absorption behavior of ammonium ions in an aqueous solution. It is also impossible to provide them with additional functions of catalysis, changes in optical responses, and so on. Although there has been a detailed study of existing adsorbents described in Non-Patent Publication 5 about the adsorption of gaseous ammonia, the adsorption capability is only limited to 10 mmol/g at 100 kPa.